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• 191. [Article] Increasing the productivity of a small yarder : crew size, skidder swinging, hot thinning

  The production rates and costs of harvesting smallwood were determined for a small yarder (Koller K-300) operating under variable conditions: the size of the crew, the addition of a skidder to swing logs ...

  Citation × Citation Citation Abstract Copy Title: Increasing the productivity of a small yarder : crew size, skidder swinging, hot thinning Author: Olsen, Eldon D., Kellogg, L. D. (Loren D.), Oregon State University. Forest Research Laboratory The production rates and costs of harvesting smallwood were determined for a small yarder (Koller K-300) operating under variable conditions: the size of the crew, the addition of a skidder to swing logs from the landing, and the type of harvest method-employed, either conventional or hot thinning (simultaneous felling and yarding of whole trees). Regression equations are presented for the felling, yarding, swinging, and loading cycles of each harvest method. Title: Increasing the productivity of a small yarder : crew size, skidder swinging, hot thinning Author: Olsen, Eldon D., Kellogg, L. D. (Loren D.), Oregon State University. Forest Research Laboratory The production rates and costs of harvesting smallwood were determined for a small yarder (Koller K-300) operating under variable conditions: the size of the crew, the addition of a skidder to swing logs from the landing, and the type of harvest method-employed, either conventional or hot thinning (simultaneous felling and yarding of whole trees). Regression equations are presented for the felling, yarding, swinging, and loading cycles of each harvest method. Close

• 192. [Article] Predicting the economic impacts of intensified forest management : Douglas County, Oregon, as a case study

  A model consisting of a linked series of equations is presented for estimating the future effect of various intensities of forest management on the economy of a region. The model, in conjunction with the ...

  Citation × Citation Citation Abstract Copy Title: Predicting the economic impacts of intensified forest management : Douglas County, Oregon, as a case study Author: Tedder, Philip L., Dippon, Duane R., Oregon State University. Forest Research Laboratory A model consisting of a linked series of equations is presented for estimating the future effect of various intensities of forest management on the economy of a region. The model, in conjunction with the most recent inventory of the USDA Forest Service, is then applied to data from Douglas County, Oregon. Results indicate that intensive forest management will have little economic impact on Douglas County over the next five decades. Title: Predicting the economic impacts of intensified forest management : Douglas County, Oregon, as a case study Author: Tedder, Philip L., Dippon, Duane R., Oregon State University. Forest Research Laboratory A model consisting of a linked series of equations is presented for estimating the future effect of various intensities of forest management on the economy of a region. The model, in conjunction with the most recent inventory of the USDA Forest Service, is then applied to data from Douglas County, Oregon. Results indicate that intensive forest management will have little economic impact on Douglas County over the next five decades. Close

• 193. [Article] Private timber harvest potential in Eastern Oregon

  Growing stock inventory on industrial and nonindustrial private forest (NIPF) lands in eastern Oregon has declined over the past 20 yr, as harvesting and mortality losses to insects and disease have outpaced ...

  Citation × Citation Citation Abstract Copy Title: Private timber harvest potential in Eastern Oregon Author: Latta, Gregory S., Oregon State University. Forest Research Laboratory, Adams, Darius Mainard, 1944- Growing stock inventory on industrial and nonindustrial private forest (NIPF) lands in eastern Oregon has declined over the past 20 yr, as harvesting and mortality losses to insects and disease have outpaced growth. Over the same time period, harvest rates on private lands have varied, with no distinct trend to the variation. In the most recent survey (1999), industrial and NIPF inventories differed by less than 8% (1.786 billion ft³ versus 1.655 billion ft³), while the NIPF timberland base was only two-thirds of the industrial base (1.105 million ac versus 1.603 million ac). This study employs recent inventories and even-flow and market-based harvest simulators to develop projections of future harvest potentials. For industrial lands, even-flow and market-based projections of future harvest potential over the next 50 yr are approximately half of average harvests over the past 40 yr. For NIPF lands the even-flow projection is 20% higher than the historical harvest average, while the market-based projection indicates potential for a substantial but short-lived increase in near-term harvest. Inventories on industrial lands rise under both projections, while NIPF inventories remain fairly stable. Continued loss of land from NIPF ownerships to other owners and uses has limited influence on the market-based NIPF harvest projection until after 2050. A simulated policy of expanded riparian protection zones reduces harvest on both ownerships roughly in proportion to the area removed from the harvestable land base. A simulated requirement to retain 30% more residual volume in partially cut stands reduces harvest by 5% on combined private ownerships and increases total inventory by 13% after 50 yr. Title: Private timber harvest potential in Eastern Oregon Author: Latta, Gregory S., Oregon State University. Forest Research Laboratory, Adams, Darius Mainard, 1944- Growing stock inventory on industrial and nonindustrial private forest (NIPF) lands in eastern Oregon has declined over the past 20 yr, as harvesting and mortality losses to insects and disease have outpaced growth. Over the same time period, harvest rates on private lands have varied, with no distinct trend to the variation. In the most recent survey (1999), industrial and NIPF inventories differed by less than 8% (1.786 billion ft³ versus 1.655 billion ft³), while the NIPF timberland base was only two-thirds of the industrial base (1.105 million ac versus 1.603 million ac). This study employs recent inventories and even-flow and market-based harvest simulators to develop projections of future harvest potentials. For industrial lands, even-flow and market-based projections of future harvest potential over the next 50 yr are approximately half of average harvests over the past 40 yr. For NIPF lands the even-flow projection is 20% higher than the historical harvest average, while the market-based projection indicates potential for a substantial but short-lived increase in near-term harvest. Inventories on industrial lands rise under both projections, while NIPF inventories remain fairly stable. Continued loss of land from NIPF ownerships to other owners and uses has limited influence on the market-based NIPF harvest projection until after 2050. A simulated policy of expanded riparian protection zones reduces harvest on both ownerships roughly in proportion to the area removed from the harvestable land base. A simulated requirement to retain 30% more residual volume in partially cut stands reduces harvest by 5% on combined private ownerships and increases total inventory by 13% after 50 yr. Close

• 194. [Article] Timber harvest projections for private land in western Oregon

  In this analysis, volume-flow and market-based models of the western Oregon timber sector are developed. The volume-flow model finds the maximum, long-term, even-flow level of cut for each ownership (industry ...

  Citation × Citation Citation Abstract Copy Title: Timber harvest projections for private land in western Oregon Author: Van Nalts, Adrienne, Latta, Gregory S., Schillinger, Randall R., Oregon State University. Forest Research Laboratory, Adams, Darius Mainard, 1944- In this analysis, volume-flow and market-based models of the western Oregon timber sector are developed. The volume-flow model finds the maximum, long-term, even-flow level of cut for each ownership (industry and non-industrial private forest). The market model simulates the interaction of log demand and timber owner supply to find the market balancing harvest quantity and log price. In both models, owner decisions on the intensity of timber management (silviculture) are made within the models consistent with owner objectives (volume or wealth maximization). Model projections suggest that western Oregon forest industry owners could sustain cut at recent (1995–1999) levels, stemming the 40-yr declining trend in their harvest. Nonindustrial private forest owners could raise harvests to near historical peak levels. These harvests could be maintained over the next five decades with no reduction in the growing stock inventory. Management would continue to shift toward the more intensive forms on both ownerships. The average age of the inventory would decline over the projection. Simulated riparian protection policies lower harvest roughly in proportion to the land base reduction and raise log prices. A policy to increase the minimum age of clearcut harvests would lead to large near-term reductions in industrial harvest but less marked reductions on NIPF lands. Prices would rise sharply in the near term. Over the longer term, the policy would act to expand inventory, raising harvest, and to depress prices. Title: Timber harvest projections for private land in western Oregon Author: Van Nalts, Adrienne, Latta, Gregory S., Schillinger, Randall R., Oregon State University. Forest Research Laboratory, Adams, Darius Mainard, 1944- In this analysis, volume-flow and market-based models of the western Oregon timber sector are developed. The volume-flow model finds the maximum, long-term, even-flow level of cut for each ownership (industry and non-industrial private forest). The market model simulates the interaction of log demand and timber owner supply to find the market balancing harvest quantity and log price. In both models, owner decisions on the intensity of timber management (silviculture) are made within the models consistent with owner objectives (volume or wealth maximization). Model projections suggest that western Oregon forest industry owners could sustain cut at recent (1995–1999) levels, stemming the 40-yr declining trend in their harvest. Nonindustrial private forest owners could raise harvests to near historical peak levels. These harvests could be maintained over the next five decades with no reduction in the growing stock inventory. Management would continue to shift toward the more intensive forms on both ownerships. The average age of the inventory would decline over the projection. Simulated riparian protection policies lower harvest roughly in proportion to the land base reduction and raise log prices. A policy to increase the minimum age of clearcut harvests would lead to large near-term reductions in industrial harvest but less marked reductions on NIPF lands. Prices would rise sharply in the near term. Over the longer term, the policy would act to expand inventory, raising harvest, and to depress prices. Close

• 195. [Article] Enhanced diameter-growth-rate equations for undamaged and damaged trees in southwest Oregon

  Equations for predicting the 5-yr diameter-growth rate of a tree are presented for eight conifer and nine hardwood tree species from southwest Oregon. Equation parameters for undamaged and damaged trees ...

  Citation × Citation Citation Abstract Copy Title: Enhanced diameter-growth-rate equations for undamaged and damaged trees in southwest Oregon Author: Hanus, Mark L., Oregon State University. Forest Research Laboratory, Hann, David W. Equations for predicting the 5-yr diameter-growth rate of a tree are presented for eight conifer and nine hardwood tree species from southwest Oregon. Equation parameters for undamaged and damaged trees combined were estimated by weighted nonlinear regression. The resulting equation for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] explained more than 71% of the variation when validated against an independent data set. These equations are being incorporated into the new edition of ORGANON for southwest Oregon, a model for predicting the development of stands. The equations extend the previous model to older stands and stands with a larger component of hardwood. We explored the effects of specific damaging agents on the 5-yr diameter-growth rates of the five most frequently encountered species and estimated damage correction factors. Damaging agents can impact 5-yr diameter-growth rate significantly and, as a result, can lead over time to diversification in stand structure. Therefore, full characterization of stand development should include prediction of the presence and frequency of the agents damaging trees within the stand and their impact on tree attributes such as total height, height-to-crown-base, diameter-growth rate, height-growth rate, and mortality rate. Title: Enhanced diameter-growth-rate equations for undamaged and damaged trees in southwest Oregon Author: Hanus, Mark L., Oregon State University. Forest Research Laboratory, Hann, David W. Equations for predicting the 5-yr diameter-growth rate of a tree are presented for eight conifer and nine hardwood tree species from southwest Oregon. Equation parameters for undamaged and damaged trees combined were estimated by weighted nonlinear regression. The resulting equation for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] explained more than 71% of the variation when validated against an independent data set. These equations are being incorporated into the new edition of ORGANON for southwest Oregon, a model for predicting the development of stands. The equations extend the previous model to older stands and stands with a larger component of hardwood. We explored the effects of specific damaging agents on the 5-yr diameter-growth rates of the five most frequently encountered species and estimated damage correction factors. Damaging agents can impact 5-yr diameter-growth rate significantly and, as a result, can lead over time to diversification in stand structure. Therefore, full characterization of stand development should include prediction of the presence and frequency of the agents damaging trees within the stand and their impact on tree attributes such as total height, height-to-crown-base, diameter-growth rate, height-growth rate, and mortality rate. Close

• 196. [Article] Animal damage to coniferous plantations in Oregon and Washington. pt. II, an economic evaluation

  Regression models of height growth and survival were fitted to aggregate data for trees, protected and not protected from animal damage, that had been surveyed on Douglas-fir and ponderosa pine plantations ...

  Citation × Citation Citation Abstract Copy Title: Animal damage to coniferous plantations in Oregon and Washington. pt. II, an economic evaluation Author: Kao, Chiang, Brodie, J. Douglas (John Douglas), 1938-, Oregon State University. Forest Research Laboratory, Black, Hugh C., 1941-, Dimock, Edward J., Evans, James, 1930-, Rochelle, James Arthur, 1942- Regression models of height growth and survival were fitted to aggregate data for trees, protected and not protected from animal damage, that had been surveyed on Douglas-fir and ponderosa pine plantations in Oregon and Washington. Animal damage significantly affected both height and survival. Dynamic programming analysis-using both soil expectation (Se) and allowable cut effect (ACE) indicators-was used to derive (1) optimal economic regimes for managing stands with full and depressed stocking levels, (2) management guidelines for protection expenditure and stand replacement, and (3) physical impacts on volume yield. At current rates of planting in Oregon and Washington and at a 3 percent discount rate, animals cause an estimated $60 million annually in damage, reducing the net capitalized value of the timber resource by $1.8 billion. Likewise, present net worth decreases by 18 percent, and growth and yield by 13 percent. Several other discount rates showed different proportional impacts from animal damage. Title: Animal damage to coniferous plantations in Oregon and Washington. pt. II, an economic evaluation Author: Kao, Chiang, Brodie, J. Douglas (John Douglas), 1938-, Oregon State University. Forest Research Laboratory, Black, Hugh C., 1941-, Dimock, Edward J., Evans, James, 1930-, Rochelle, James Arthur, 1942- Regression models of height growth and survival were fitted to aggregate data for trees, protected and not protected from animal damage, that had been surveyed on Douglas-fir and ponderosa pine plantations in Oregon and Washington. Animal damage significantly affected both height and survival. Dynamic programming analysis-using both soil expectation (Se) and allowable cut effect (ACE) indicators-was used to derive (1) optimal economic regimes for managing stands with full and depressed stocking levels, (2) management guidelines for protection expenditure and stand replacement, and (3) physical impacts on volume yield. At current rates of planting in Oregon and Washington and at a 3 percent discount rate, animals cause an estimated $60 million annually in damage, reducing the net capitalized value of the timber resource by $1.8 billion. Likewise, present net worth decreases by 18 percent, and growth and yield by 13 percent. Several other discount rates showed different proportional impacts from animal damage. Close

• 197. [Article] Production rates and costs for yarding by cable, balloon, and helicopter compared for clearcuttings and partial cuttings

  This report supplements Research Bulletin 18 (1975) of the Forest Research Laboratory, School of Forestry, Oregon State University. Bulletin 18 summarized analyses of data for the first field season of ...

  Citation × Citation Citation Abstract Copy Title: Production rates and costs for yarding by cable, balloon, and helicopter compared for clearcuttings and partial cuttings Author: Dykstra, Dennis P., Oregon State University. Forest Research Laboratory This report supplements Research Bulletin 18 (1975) of the Forest Research Laboratory, School of Forestry, Oregon State University. Bulletin 18 summarized analyses of data for the first field season of the Pansy Basin Study. This Bulletin extends those analyses to the second, and final, field season. Time-study observations during the second field season were made of three yarding systems: running skyline, balloon haulback, and heavy-lift helicopter. The running skyline was observed in a partial cutting, the balloon in a clearcutting, and the helicopter in both clearcuttings and partial cuttings. All of the cutting units were designed to reduce damage to the appearance of the landscape. Results of the analyses suggest that productive yarding time is a function of yarding distance, volume per turn and per log, chordslope, and numbers of logs or chokers per turn. For the running skyline and the balloon, lateral yarding distance was also an important determinant of productive yarding time. In addition, the number of men in the rigging crew was found to be a statistically significant predictor for the running skyline, as was tagline length for the balloon. For the running skyline system, the data in this study support the hypothesis that yarding production rates are significantly influenced by silvicultural treatment. For the helicopter, however, no significant difference appeared in yarding rates between the clearcutting and partial cutting treatments. The effect of cutting unit design on yarding efficiency for cable systems cannot be generalized, although it did not appear to be significant for the cutting units in the Pansy Basin Study. Certainly, cutting units can be designed for which unit shape is an important determinant of cable yarding productivity. Shape of cutting unit would not be expected to influence helicopter yarding productivity, however. Title: Production rates and costs for yarding by cable, balloon, and helicopter compared for clearcuttings and partial cuttings Author: Dykstra, Dennis P., Oregon State University. Forest Research Laboratory This report supplements Research Bulletin 18 (1975) of the Forest Research Laboratory, School of Forestry, Oregon State University. Bulletin 18 summarized analyses of data for the first field season of the Pansy Basin Study. This Bulletin extends those analyses to the second, and final, field season. Time-study observations during the second field season were made of three yarding systems: running skyline, balloon haulback, and heavy-lift helicopter. The running skyline was observed in a partial cutting, the balloon in a clearcutting, and the helicopter in both clearcuttings and partial cuttings. All of the cutting units were designed to reduce damage to the appearance of the landscape. Results of the analyses suggest that productive yarding time is a function of yarding distance, volume per turn and per log, chordslope, and numbers of logs or chokers per turn. For the running skyline and the balloon, lateral yarding distance was also an important determinant of productive yarding time. In addition, the number of men in the rigging crew was found to be a statistically significant predictor for the running skyline, as was tagline length for the balloon. For the running skyline system, the data in this study support the hypothesis that yarding production rates are significantly influenced by silvicultural treatment. For the helicopter, however, no significant difference appeared in yarding rates between the clearcutting and partial cutting treatments. The effect of cutting unit design on yarding efficiency for cable systems cannot be generalized, although it did not appear to be significant for the cutting units in the Pansy Basin Study. Certainly, cutting units can be designed for which unit shape is an important determinant of cable yarding productivity. Shape of cutting unit would not be expected to influence helicopter yarding productivity, however. Close

• 198. [Article] Log-scale and lump-sum timber selling on federal lands in western Oregon

  Considerable interest has arisen in the relation between timber-selling procedures and the accomplishment of timber-selling objectives on public lands in the West. Procedures of public agencies for measuring ...

  Citation × Citation Citation Abstract Copy Title: Log-scale and lump-sum timber selling on federal lands in western Oregon Author: Arney, James Douglas, 1941-, Beuter, John H., Oregon State University. Forest Research Laboratory Considerable interest has arisen in the relation between timber-selling procedures and the accomplishment of timber-selling objectives on public lands in the West. Procedures of public agencies for measuring and paying for timber by log scale or by lump sum have attracted special attention. There are significant differences in the two procedures. In log-scale timber selling, an estimate is made of the volume of merchantable timber in the standing trees on the tract to be sold. The purchaser agrees to pay a specific amount for each unit of merchantable volume he removes from the tract. That is, each tree or portion of a tree removed from the tract is measured (scaled) and the purchaser pays only for the merchantable volume he actually removes. In lump-sum timber selling, an estimate is made of the volume of merchantable timber in the standing trees on the tract to be sold. The purchaser agrees to pay a specific amount for the entire tract. He pays no more nor less than that amount, no matter how much merchantable timber he actually removes from the tract. Thus, the amount a purchaser pays and the seller receives for the timber will vary between the two procedures depending on the accuracy of measurement and the extent to which the purchaser cuts and removes volume from the tract (Table 1). Merits and shortcomings of the two procedures have been debated at great length. Arguments for and against the two procedures are heard frequently-not all are necessarily valid. Title: Log-scale and lump-sum timber selling on federal lands in western Oregon Author: Arney, James Douglas, 1941-, Beuter, John H., Oregon State University. Forest Research Laboratory Considerable interest has arisen in the relation between timber-selling procedures and the accomplishment of timber-selling objectives on public lands in the West. Procedures of public agencies for measuring and paying for timber by log scale or by lump sum have attracted special attention. There are significant differences in the two procedures. In log-scale timber selling, an estimate is made of the volume of merchantable timber in the standing trees on the tract to be sold. The purchaser agrees to pay a specific amount for each unit of merchantable volume he removes from the tract. That is, each tree or portion of a tree removed from the tract is measured (scaled) and the purchaser pays only for the merchantable volume he actually removes. In lump-sum timber selling, an estimate is made of the volume of merchantable timber in the standing trees on the tract to be sold. The purchaser agrees to pay a specific amount for the entire tract. He pays no more nor less than that amount, no matter how much merchantable timber he actually removes from the tract. Thus, the amount a purchaser pays and the seller receives for the timber will vary between the two procedures depending on the accuracy of measurement and the extent to which the purchaser cuts and removes volume from the tract (Table 1). Merits and shortcomings of the two procedures have been debated at great length. Arguments for and against the two procedures are heard frequently-not all are necessarily valid. Close

• 199. [Article] Animal damage to coniferous plantations in Oregon and Washington. pt.1, a survey, 1963-1975

  Mammal and bird damage recorded on Douglas-fir and ponderosa pine plots-randomly established in Oregon and Washington during 1963-64, then observed for 5 to 10 years-was evaluated for impact on survival ...

  Citation × Citation Citation Abstract Copy Title: Animal damage to coniferous plantations in Oregon and Washington. pt.1, a survey, 1963-1975 Author: Oregon State University. Forest Research Laboratory, Black, Hugh C., 1941-, Dimock, Edward J., Evans, James, 1930-, Rochelle, James Arthur, 1942- Mammal and bird damage recorded on Douglas-fir and ponderosa pine plots-randomly established in Oregon and Washington during 1963-64, then observed for 5 to 10 years-was evaluated for impact on survival and growth. In all, 194 plots were installed, and 10 of the 110 seedlings on each plot were caged to protect them from animals. All trees were examined after planting and after bud burst each year for 5 years. A selected sample of 45 Douglas-fir plots was observed another 5 years for long-term patterns and effects of severe plantation damage. Survival and growth were compared for caged and uncaged trees. The agents, kind, amount, and distribution of animal damage were evaluated by state, by subregion, and by relation to site features. Results indicate that stand damage in plantations exposed to heavy animal use, especially during seedling establishment, warrants expenditure for protective measures. Title: Animal damage to coniferous plantations in Oregon and Washington. pt.1, a survey, 1963-1975 Author: Oregon State University. Forest Research Laboratory, Black, Hugh C., 1941-, Dimock, Edward J., Evans, James, 1930-, Rochelle, James Arthur, 1942- Mammal and bird damage recorded on Douglas-fir and ponderosa pine plots-randomly established in Oregon and Washington during 1963-64, then observed for 5 to 10 years-was evaluated for impact on survival and growth. In all, 194 plots were installed, and 10 of the 110 seedlings on each plot were caged to protect them from animals. All trees were examined after planting and after bud burst each year for 5 years. A selected sample of 45 Douglas-fir plots was observed another 5 years for long-term patterns and effects of severe plantation damage. Survival and growth were compared for caged and uncaged trees. The agents, kind, amount, and distribution of animal damage were evaluated by state, by subregion, and by relation to site features. Results indicate that stand damage in plantations exposed to heavy animal use, especially during seedling establishment, warrants expenditure for protective measures. Close

• 200. [Article] Diameter growth equations for Douglas-fir and grand fir in the western Willamette Valley of Oregon

  "Equations for predicting diameter growth are an essential component of single-tree growth and yield models (Munro 1974). Diameter growth predictions are used to characterize individual-tree development ...

  Citation × Citation Citation Abstract Copy Title: Diameter growth equations for Douglas-fir and grand fir in the western Willamette Valley of Oregon Author: Zumrawi, Abdel Azim, Oregon State University. Forest Research Laboratory, Hann, David W. "Equations for predicting diameter growth are an essential component of single-tree growth and yield models (Munro 1974). Diameter growth predictions are used to characterize individual-tree development and to project the growth of stand basal area and volume. Both diameter growth and basal area growth have been used as the dependent variable in modeling the development of a tree's diameter (Holdaway 1984, Ritchie and Hann 1985, Wykoff 1986, Wensel et al. 1987, Dolph 1988). The choice of which dependent variable to use has usually been suggested by the data, including the behavior of the residuals and the goodness-of-fit of the resulting equations. Ritchie and Hann (1985) developed nonlinear basal-area growth equations for Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis). It was intended that the equations would be used to predict individual- tree diameter growth in the western Willamette Valley version of ORGANON (Hann et al. 1992). However, Hann and Larsen (1991) found that using a basal-area growth equation to predict diameter growth could result in erratic and unreasonable predictions of diameter growth for trees with small diameters. Therefore, the objective of the present study was to develop diameter growth equations for Douglas-fir and grand fir in the western Willamette Valley of Oregon by using the equation form of Hann and Larsen (1991)."--Introduction Title: Diameter growth equations for Douglas-fir and grand fir in the western Willamette Valley of Oregon Author: Zumrawi, Abdel Azim, Oregon State University. Forest Research Laboratory, Hann, David W. "Equations for predicting diameter growth are an essential component of single-tree growth and yield models (Munro 1974). Diameter growth predictions are used to characterize individual-tree development and to project the growth of stand basal area and volume. Both diameter growth and basal area growth have been used as the dependent variable in modeling the development of a tree's diameter (Holdaway 1984, Ritchie and Hann 1985, Wykoff 1986, Wensel et al. 1987, Dolph 1988). The choice of which dependent variable to use has usually been suggested by the data, including the behavior of the residuals and the goodness-of-fit of the resulting equations. Ritchie and Hann (1985) developed nonlinear basal-area growth equations for Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis). It was intended that the equations would be used to predict individual- tree diameter growth in the western Willamette Valley version of ORGANON (Hann et al. 1992). However, Hann and Larsen (1991) found that using a basal-area growth equation to predict diameter growth could result in erratic and unreasonable predictions of diameter growth for trees with small diameters. Therefore, the objective of the present study was to develop diameter growth equations for Douglas-fir and grand fir in the western Willamette Valley of Oregon by using the equation form of Hann and Larsen (1991)."--Introduction Close